The evil mystics wouldn't take on a pupil for the very reasoning that they are evil and covet the power for themselves.
Also, which of them wouldn't see an acolyte for a potential threat? Someone who would (because THE VILLAIN certainly would) turn on their teacher and usurp their power?
No.
It's just bad fiction to think that a true evil would try to cultivate another in their midst - at least not without some sort of "security" provision (a death switch of some sort).
Legacies are a possible exception: a father trying to lure his son to the "family business" so to speak.
But that doesn't usually turn out well, almost always ending in fratricide or the turning of the son to the side of the angels (or the less likely turning of the father to good).
See how it worked for Darth Vader?
Heroes mostly seek out pupils for two reasons:
1) to help a young talent reach their potential
2) to seek to broaden the base of good with which to battle evil (especially if the hero needs someone to carry on in their stead)
Villains don't care if anyone gets any better (especially not better than them) and they don't look to have help, as they want sole credit in killing the hero, want no "governors" when ruling the world - and see no time when they won't be around to do what they wilt.
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